Off-CenteredDroplet Impact on a Single-Triangular-RidgeSuperhydrophobic Surface

After droplet impact, asymmetric retraction is beneficial for reducing contact time. This work conducts numerical simulations to investigate the morphological evolution and contact time of droplets on a single-triangular-ridge superhydrophobic surface following off-centered impact. Based on the observed morphological evolution, droplet behaviors are categorized into five types according to the off-centered distance. A theoretical classification model is proposed to predict the ranges of off-centered distances for different types. The effects of the Weber number and off-centered distance on the contact time, along with the underlying reasons, are explored. The resultant spreading, contraction, and splitting processes are analyzed, and the potential mechanisms for contact time reduction are elucidated by quantifying droplet shape and characteristic time. A theoretical model for predicting the contact time of a subdroplet under splitting conditions is explained. Off-centered-induced asymmetry and ridge compression significantly alter the droplet velocity distribution. At small off-centered distances, ridge compression directs a larger portion of the droplet to spread along it, greatly affecting the spreading duration. Contact time is primarily determined by retraction time. These findings are expected to clarify the basics of asymmetric bouncing on a ridge and provide useful guidance for self-cleaning and anti-icing strategies.